As part of build infrastructure migrations, we've been running builds side-by-side on the old Buildbot infrastructure and new LUCI infrastructure. Part of the motivations behind LUCI are to have cleaner bot managing, e.g. not performing bot-specific modifications.

One of the side-by-side builds (https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Win%207%20Tests%20x64%20(1)/45) fails on MouseEventsTest.TestOnMouseOut:

[ RUN      ] MouseEventsTest.TestOnMouseOut
[2376:4360:0417/130857.915:ERROR:install_util.cc(589)] Unable to create registry key HKLM\SOFTWARE\Policies\Chromium for reading result=2
[2376:3772:0417/130857.962:WARNING:discovery_network_list_win.cc(195)] Failed to open Wlan client handle: 1062
[2376:4360:0417/130857.962:WARNING:chrome_browser_main_win.cc(630)] Command line too long for RegisterApplicationRestart:  --brave-new-test-launcher --cfi-diag=0 --gtest_also_run_disabled_tests --gtest_filter=MouseEventsTest.TestOnMouseOut --single_process --snapshot-output-dir="e:\b\s\w\iogx4wt7" --test-launcher-bot-mode --test-launcher-output="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir3088_10040\results3088_13195\test_results.xml" --test-launcher-summary-output="e:\b\s\w\iogx4wt7\output.json" --user-data-dir="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir3088_10040\d3088_21026" --disable-offline-auto-reload --no-first-run --no-default-browser-check --enable-logging=stderr --disable-default-apps --wm-window-animations-disabled --disable-component-update --test-type=browser --force-color-profile=srgb --disable-zero-browsers-open-for-tests --ipc-connection-timeout=30 --allow-file-access-from-files --dom-automation --log-gpu-control-list-decisions --disable-backgrounding-occluded-windows --disable-gl-drawing-for-tests --override-use-software-gl-for-tests --force-color-profile=srgb --disable-compositor-ukm-for-tests --enable-features=TestFeatureForBrowserTest1 --disable-features=NetworkPrediction,TestFeatureForBrowserTest2 --flag-switches-begin --flag-switches-end --restore-last-session about:blank
[2376:4360:0417/130858.094:INFO:mouse_events_interactive_uitest.cc(43)] Waiting for title: onload

Some of the failing behavior is known (Issue 419468  #16 , and this test has been flaky for a while and is mostly disabled already); what's new is the attempt (and failure) to create a registry key HKLM\SOFTWARE\Policies\Chromium, which appears to be related to a recent feature (crrev.com/8327d5a7).

Creating a registry key for mouse events tests seems odd. If this behavior is indeed unexpected, that dependency should be removed. If it is expected, then the registry keys need to be rewired, e.g. via virtualizing, such that they're not set directly on the bots.*

Tentatively assigning to rogerta@, and please add/re-componentize as appropriate!

*Note that the difference of registry creation happens on LUCI but not Buildbot. The main difference between the two is that LUCI builds do not change bot state. If Buildbot is attempting --- and succeeding --- to create registry keys, that would explain why the Buildbot builds are green, but which eventually leads to an unmaintainable state, so simply writing the key directly is not an option.